Compact multi-aperture and in particular dual-aperture (also referred to as “dual-lens” or “dual-camera”) digital cameras are known. Miniaturization technologies allow incorporation of such cameras in compact portable electronic devices such as tablets and mobile phones (the latter referred to hereinafter generically as “smartphones”), where they provide advanced imaging capabilities such as zoom, see e.g. co-owned PCT patent application No. PCT/IB2013/060356 titled “High-resolution thin multi-aperture imaging systems”, which is incorporated herein by reference in its entirety. A two-camera system (exemplarily including a wide-angle (or “Wide”) camera and a telephoto (or “Tele”) camera) is calibrated in an end product (e.g. in a smartphone) after manufacturing.
System calibration matches Tele and Wide image pixels by capturing in both cameras known objects. This enables faster and more reliable application of fusion between the two cameras, as described in PCT/IB2013/060356. One problem with such cameras may arise from mishaps such as drop impact. The latter may cause a relative movement between the two cameras after system calibration, changing the pixel matching between Tele and Wide images and thus preventing fast reliable fusion of the Tele and Wide images.
Another problem with dual-aperture zoom cameras relates to their height. There is a large difference in the height (also known as total track length or “TTL”) of the Tele and Wide cameras. The TTL, see FIG. 1, is defined as the maximal distance between the object-side surface of a first lens element and a camera image sensor plane. In the following, “W” and “T” subscripts refer respectively to Wide and Tele cameras. In most miniature lenses, the TTL is larger than the lens effective focal length (EFL), which has a meaning well known in the art, see FIG. 1. A typical TTL/EFL ratio for a given lens (or lens assembly) is around 1.3. In a single-aperture smartphone camera, EFL is typically 3.5 mm, leading to a field of view of 70-80°. Assuming one wishes to achieve a dual-aperture X2 optical zoom in a smartphone, it would be natural to use EFLW=3.5 mm and EFLT=2×EFLW=7 mm. However, without spatial restrictions, the Wide lens will have an EFLW=3.5 mm and a TTLW of 3.5×1.3=4.55 mm, while the Tele lens will have EFLT=7 mm and TTLT of 7×1.3=9.1 mm. The incorporation of a 9.1 mm lens in a smartphone camera would lead to a camera height of around 9.8 mm, which is unacceptable for many smartphone makers. Also the large height difference (approx. 4.55 mm) between the Wide and Tele cameras can cause shadowing and light-blocking problems, see FIG. 2.
A third problem relates to the implementation of standard optical image stabilization (OIS) in a dual-aperture zoom camera. Standard OIS compensates for camera tilt (“CT”) by a parallel-to-the image sensor (exemplarily in the X-Y plane) lens movement (“LMV”). Camera tilt causes image blur. The amount of LMV (in mm) needed to counter a given camera tilt depends on the cameras lens EFL, according to the relation LMV=CT*EFL where “CT” is in radians and EFL is in mm. Since as shown above a dual-aperture zoom camera may include two lenses with significantly different EFLs, it is impossible to move both lenses together and achieve optimal tilt compensation for both Tele and Wide cameras. That is, since the tilt is the same for both cameras, a movement that will cancel the tilt for the Wide camera will be insufficient to cancel the tilt for the Tele camera. Similarly, a movement that will cancel the tilt for the Tele camera will over-compensate the tilt cancellation for the Wide camera. Assigning a separate OIS actuator to each camera can achieve simultaneous tilt compensation, but at the expense of a complicated and expensive camera system.